In conventional sewing machines there are employed various reciprocal motion mechanisms such as a reciprocal linear motion mechanism a rocking motion mechanism. In such mechanisms, as the sewing machine is operated at a high speed, its inertia force is increased, with the result that the amount of movement tends to increase at the time of the high speed operation rather than at the time of the low speed operation. Especially, in the feed mechanisms in conventional high speed sewing machines, due to the large weight of the feed bar which supports the feed dog and is connected with the mechanism to move the feed dog back and forth and the mechanism to move it up and down, the amount of movement of the feed dog becomes larger in high speed operation than in low speed operation to provide a phenomenon of making the cloth feeding amount larger. Accordingly, the cloth feeding amount gradually increases during the time from the start of the sewing machine to the time of the high speed operation, and unevenness is apt to be produced in seams.